The standards of the family ISO 11898-1 through -5 describe the Controller Area Network (CAN), as well as an expansion of CAN referred to as Time-Triggered CAN (TTCAN). The standards are also referred to below as the CAN standard. The media access control method used in CAN is based on a bitwise arbitration. In the bitwise arbitration, a plurality of participating stations can simultaneously transmit data via the channel of the bus system without thereby disturbing the data transmission. In addition, during the transmission of a bit via the channel the participating stations can determine the logical state (0 or 1) of the channel. If a value of the sent bit does not correspond to the determined logical state of the channel, the participating station then terminates access to the channel. In CAN, the bitwise arbitration is standardly carried out on the basis of an identifier contained in a message that is to be transmitted via the channel. After a participating station has completely transmitted the identifier on the channel, it knows that it has exclusive access to the channel. Thus, the end of the transmission of the identifier corresponds to a beginning of a clearance interval within which the participating station can use the channel exclusively. According to the protocol specification of CAN, other participating stations may not access the channel, i.e., transmit data on the channel, until the transmitting participating station has transmitted a checksum field (CRC field) of the message. Thus, an end time point of the transmission of the CRC field corresponds to an end of the clearance interval.
Thus, through the bitwise arbitration a disturbance-free transmission via the channel is achieved of the message that has obtained the arbitration method. The protocols of CAN are suitable in particular for the transmission of short messages under real-time conditions, such that, through suitable assignment of the identifier, it can be ensured that particularly important messages almost always obtain the arbitration and are successfully transmitted.
With the increasing networking of modern vehicles and the introduction of additional systems for improving, for example, driver safety or driver comfort, the demands become greater on the quantities of data that are to be transmitted and on the latency times that are permissible during transmission. Examples include driving dynamics regulating systems, such as the electronic stability program ESP, driver assistance systems, such as automatic distance regulation ACC, or driver information systems such as traffic sign recognition (see, for example, the descriptions in “Bosch Kraftfahrtechnisches Handbuch,” 27th ed., 2011, Vieweg+Tuebner).
German Patent Application No. DE 103 11 395 A1 describes a system in which asynchronous serial communication can alternatively take place via an asymmetrical physical CAN protocol or via the symmetrical physical CAN protocol, and in this way a higher data transmission rate or data transmission security is achievable for the asynchronous communication.
German Patent Application No. DE 10 2007 051 657 A1 describes the use, in the exclusive time windows of the TTCAN protocol, of an asynchronous, fast, non-CAN-conforming data transmission in order to increase the transmitted data quantity.
In “Overclocking of controller area networks” (Electronics Letters, vol. 35, no. 22 (1999), page 1924, G. Cena and A. Valenzano address the effects of an overclocking of the bus frequency in sub-regions of the messages on the effectively achieved data rate.